Electromagnetic reproducer



July 1 1930- J. WEINBERGER ELECTROMAGNET I C BEPRODUCER Filed A118. 9' 1925 .EN W

I TOR JULIUS BNBE ER ATT NEY Patented July 15, 1930 UNITED .STATES J'U'IiIUS WEINBERGER,'OF NEW YORK, N. Y., ASSIGNOB IO RADIO CORPORATION OF PATENT OFFICE AMERICA, A CORPORATION OF DELAWARE ELECTROMAGNETIC REPRODUCEB Application filed August 29, 1925. Serial No. 53,422.

' The invention relates to electro-magnetic recorders or reproducers for phonographs or similar devices and has for its principal object to provide such a device which shall be free from distortion due to resonant points in the vibrating mechanism.

A more specific object of the invention is to provide an electromagnetic recorder or reproducer which causes variation of currents in an electric circuit due to vibrations of its vibratory system and which shall be free from resonant points in the vibrating system.-

Still another object of the invention is to provide a vibratory system in which the mass, resiliency and damping shall be in separate elements whereby each may be separately chosen without modifying either of the others.

till another object of the invention is to provide a vibratory system for electro-magnetic recorders or reproducers wherein undulating currents are caused by flux variation efiected by the vibratory system and which has an appropriate damping system for preventing mechanical resonance effects in the vibratory system.

Still another object of the invention is to provide an electro-magnetic recorder or re= producer in which variations of electric currents are occasioned. by changing impedance efiected by the,vibratory system and in which the vibratory system has its mass resiliency and damping each isolated in a separate element whereby each may be adjusted independently of the others.

The usual type of reproducer in phonographs consists of a needle which moves in a groove formed in the record whose bottom or sides have serrations thereon to cause vibration of the needle. The needle is {aste'ned to an arm which impin es on or is connected in some manner to a die hra m. The

' vibrations of the needle are t ere y trans- .ferred to the diaphragm causing it to emit sounds which are reproductions of those originally causing the serrations in the record grooves. The electric phonogra h is similar in its operation but instead of t e needle v1- br'ations being transferred mechanically to The reproducer, as illustrated, comprises a, 100

the diaphragm they effect current changes in an electric circuit including an electromagnet whose armature may be either the diaphra in itself ora magnetic member mechanical y connected to the diaphragm. The

present invention applies more specifically lie quality which is very annoying and ruins the artistic eii'ect of the reproduction entirely. in most of the desirable vibratory mechanisms now in use there are several such resonant periods well within the range of audibility. Now, I have discovered that by making a damping device which is aseparate entity entirely distinct from the diaphrugm and b certain improvements in the electrical details of the system ll can reproduce original sounds with an unusual degree of faithfulness and intensity and increase generally the efiiciency of operation and artistic efi'ect of the reproduction.

The invention can best be-understood by referring to the following detailed description which should be read in connection with the accompanying drawing, in which like reference characters represent the same parts in the several views and in which bllgig. .1 shows the device completely assem- Fig. 2 is a side elevation of the device with the cover plates removed.

Fig. 3 is a bottom plan view of the device. Fig. 411s a vertical'central section.

Fig. 5 is a vertical central section at right angles to the section shown in Fig. 4 and Fig. ,6 is a perspective view, the cover plates being removed to disclose the operating mechanism.

. permanent U-shaped magnet 2 to whose ends are attached the pole pieces 3 and 4. These pole pieces consist essentially of a flat rather thick late attached by screws to the U- sha e magnet at one end each having a air of ateral extensions at its free end w ose shape can be readily seen in Figs. 3, 4 and 6. The extensions on the pole piece 3 are re resented by the reference characters an 31 and those on the pole piece 4 at and 41. The extension 30 has its flat end face opposed to the flat end face of the extension 40 and the extensions 31 and 41 are similarly placed,

a small air gap being left between the opposing faces. It will be noted that the coacting pole pieces with their associated extensions outline a central cavity open at the ends in which is placed the operating coil 12. The open ends of this cavity are partiall closed by angle-shaped members 5 and 6 w 'ch are attached to the pole pieces 3 and 4 by suit able screws. These angle members serve as supports for certain operating elements of the device and should preferably 'be of nonma etic material.

he vibratory system of the device consists of a flat spring 7 to which is attached b electric welding or otherwise a flat steel bar 8.

The bar extends through the spring and has' one of its ends enlarged as at 9, this enlarged end having a cavity in which the honograph needle 10 may be clamped by the t umb screw 11. The metal spring 7 is attached to the supporting members 5 and 6 in osition to make.

the steel bar extend centra 1y through the air ga s between the extendingextensions on the po e pieces and throu h the central opening of the coil 12. In t e specific embodiment shown the spring 7 extends between the coil 12 and the lower extensions 31 and 41. It should be noted that in the arrangement thus far described substantially all the mass of the vibratory system resides in the steel bar 8 and all the resiliency in the spring 7 whereby both the mass and resiliency can be chosen independently of each other.

The arrangement thus far described without further. modification would be objectionable as the vibratory stem for the most desirable conditions woul have several mechanical resonant points within the range of audibility causing considerable distortion in.

the sound emitted. This difliculty may be overcome by adopting a suitable dam ing system and the one hereinafter described has been found to be admirable for the purpose.

The dam ing system comprises two screws 13 threads into suitable tapped holes in the le pieces and having at their inner ends soft obs 14 of rubber or other suitable material adapted to engage the steel bar 8. The damping may be varied by merely tightening or loosenin the screws 18 thereby causing the rubber kno 14 to bear a ainst the bar 8 more or less firmly. A m t od is thus prois obvious'that many di 41 and with its lon tudinal axis extendingthrough the center line of the coil 12.

The extensions 40 and 41 are of like polarity opposite to that of the lugs 30 and 31. In

its normal rest position the steel bar 8 is symmetrically located with respect to the pole pieces and will therefore have no efiect on the magnetic flux distribution. The flux under these conditions will pass between the extensions 30 and 40 and between the extensions 31 and 41, substantiall none of it inter with the coil 12. en the needle 10 v1- brates, owin to serrations on the record grooves, the Ear 8 will be displaced from its symmetrical location and its displacement will follow the Wibrations of the needle. These dis lacements of the bar Swill cause it to'flex t e spring 7 and the bar will tend to turn about t leaves its central rest position therefore its upper end will approach an u per extension 30 or40 and its lower end wil approach the 'the bar 8 from the upper extension 40, or

example, to the lower extension 31 thus cause spring as apivot. As it ing part of the flux to link with the coil 12.. i

This leakage flux will cause chan in'the impedance of the coil 12 and these 0 a es in impedance will be proportional to and ollow accuratelythe vibrations of the needle 10.

The changes in impedances of the coil 12 may be made use of to'modulate a vacuum tube oscillator andthe modulated oscillations may be detected and caused to operate a loud speaker.

The whole device after assembl may be enclosed with a cover shown at 1 in Fig. 1. The cover must leave the needle 10 e so that it will be free to vibrate and 0 cover should preferably have holes shown at 15 therein through which the heads of the adjusting screws 13 may be reached to permit of adjusting the damping without removing the cover.

. t it obvious that the device can also be used was reproducer, the on] essential beinginthe needle or us. Inthiscaeethe undulating currents in the actuat' coil will causevibrations of the needle causing it to cut sound impressions in the record groove!- While 'Lhave disclosed my invention in connection with a very sieeific embodiment it ere ing it will readily occur to those skilled in the art and I intend the invention to be limited only as indicated by the scope of the following clalms.

1 claim:

1. In a phonograph reproducer, a laterally twistable spring blade supported at its ends, and a needle arm secured to and supported by said blade which also forms a solid pivot bearing for said arm.

2. A phonograph reproducer comprising a permanent magnet, a pole piece for each pole of said permanent magnet, a pair of extensions on each pole piece, said pole pieces being positioned to form air gaps between the extensions on one pole piece and the extensions on the other pole piece, an armature positioned in said air gaps, a winding positioned between said extensions and arranged to surround said armature, a pivot for said armature located between said winding and the air gap formed by one of the extensions on each of said pole pieces, and means for vibrating said armature.

3. A phonograph reproducer comprising means for providing a magnetic field, pole pieces for said means, extensions on said pole pieces, an armature positioned adjacent said extensions, a winding surrounding said armature and positioned between said extenslons, and a spring member secured to said armature to form a pivot therefor, said spring member being positioned between said winding and one of the extensions on each of said pole pieces.

4. A phonograph reproducer comprising an armature, means for vibrating said armature, said means being attached to one end of said armature, means for providing a magnetic field, a pole piece for the last mentioned means, a pair of extensions on said pole piece, said extensions terminating near the ends of said armature and out of contact therewith, a winding surrounding said armature and positioned between said extensions, a spring blade pivot member secured to said armature and positioned adjacent one of said extensions, and means for damping vibrations of. said armature and for limiting its movement positioned to contact with the other end of said armature.

5. A phonograph reproducer comprising means for providing a magnetic field, a pair of pole pieces for said means, a plurality of extensions on each pole piece, said pole pieces being arranged so that the extensions on one pole piece form pairs with the extensions on the other pole piece, an armature positioned between said pairs of extensions and out of contact therewith, and a pivot for said armature positioned adjacent one of said pairs of extensions.

6. A phonograph reproducer comprising a member for providing a magnetic field, a pair of pole pieces for said member, two extensions on each pole piece, said pole pieces being arranged so that the extenslons on one pole piece form pairs with the extensions on the other pole piece, an armature positioned between said pairs of extensions and out of contact therewith, and a flat spring pivot member secured to said armature and positioned immediately adjacent one of said pairs of extensions.

7. A magnet system for a phonograph re producer comprising a permanent magnet, pole pieces for said magnet, an armature positioned between said pole pieces, means for vibrating said armature, said means being attached to one end of said armature, and pivot means for said armature, said pivot means being positioned to contact with said armature at a point substantially one-third of its length from the end to which the means for vibrating the armature is attached.

8. A magnet system for a phonograph reproducer comprising a permanent magnet, pole pieces for said magnet, an armature positioned between said pole pieces, means for vibrating said armature, said means being attached to one end of said armature, angle members attached to said pole pieces, a flat spring blade secured at its ends to said angle members, said spring blade being secured at an intermediate point to said armature and forming a solid pivot for said armature, and damping means for reducing the vibrations of said armature, said damping means comprising a screw member threaded in each of said pole pieces and provided at its end with yielding material for contacting with the other end of said armature.

JULIUS WEIN BERGER. 

